1. Field of the Invention
The present invention relates to an output circuit for a player, and more particularly, to an output circuit of a player capable of detecting whether a cable is electrically connected to an output port of the output circuit.
2. Description of the Prior Art
In modern society, various kind of video or audio information is stored and recorded in electrical, magnetic or optical media. Accessing this stored information involves using video or audio players to read and transform data into electrical signals and then display these images or play this sound through video or audio media. Display media directly relate to the quality of their output video or audio signals so engineers make effort to improve video or audio players.
Please refer to FIG. 1. FIG. 1 illustrates function blocks of a conventional player by using an example of a CD player 10. The CD player 10 comprises an access circuit 12, an output circuit 14 and an output end 26. Generally speaking, modern players comprise a plurality of outputs and FIG. 1 shows one output end as a representative for convenience. If being plugged into the video/audio apparatus 18, the output end 26 is connected to the video/audio apparatus 18(for example, a TV) through the corresponding output cable 16. The CD player 10 reads the stored video/audio signals from the CD 20C, and transmits these signals to the video/audio apparatus 18 by the output end 26 and the output cable 16. To complete the above procedure, the access circuit 12 comprises a motor 20A and a reading head 20B. The CD 20C is driven to rotate and the reading head 20B read the stored data in the CD 20C. These data are decoded or demodulated and then become digital information signals 21A that are transmitted to the output circuit 14. There is a signal circuit 22 and an output port 24 corresponding to output end 26 in the conventional circuit 14. The signal circuit 22 can transform information signals 21A to output signals 21B that are properly adjusted for outputting. For example, signal circuits 22 can be a TV DAC (television digital-to-analog converter) that transforms digital information signals 21A to output signals 21B of suitable levels and output power. Through the output port 24 of the output circuit 14 and the output end 26, the output signals 21B can be transmitted to the video/audio apparatus 18 by the output cable 16 and the video/audio apparatus 18 shows images/sounds from these signals.
As mentioned above, modern video/audio players comprise a plurality of output ends for flexibility of application. However, an ordinary user would use some output ends for transmitting video/audio signals, while the other output ends are not used. Because the signal circuit 22 consumes some power when outputting the output signal 21B, if the corresponding output end 26 is not connected any video/audio apparatus but keeps outputting output signals 21B, power is wasted. To solve this problem, the conventional player 10 is equipped with a mechanically-driven switch 28 connected to the output end 26 outside the output circuit 14 in order to detect if the output end 26 is connected to the output cable 16 in a mechanical way.
In the conventional player apparatus 10, the operation principles of the mechanically-driven switch 28 are described in the following. When the output cable 16 is plugged in the output end 26, the end point of the output cable 16 will trigger the mechanically-driven switch 28 and the mechanically-driven switch 28 will feedback an electrical signal to the output circuit 14. The signal controlling circuit 22 processes the signal and outputs the output signals 21B to the output 24. Comparatively, when the output cable 16 is not connected to the output end 26, the mechanically-driven switch 28 will detect that the output end 26 connects to nothing. The mechanically-driven switch 28 will stop the signal controlling circuit 22 with the other electrical signal.
With the mechanically-driven switch 28, the player apparatus 10 can detect if the output end 26 connects the output cable 16. However, this prior art has some disadvantages. First, the mechanically-driven switch 28 is involved in integration of mechanical/electrical devices so the manufacturing procedures are complicated. It is both time-consuming and money-wasting. In addition, the mechanically-driven switch 28 detects connection of the output cable in a mechanical way so that plugging action wears down the apparatus and makes the display apparatus operate incorrectly. Third, functions of the output circuit 14 are often implemented by a chip, but the output circuit 14 must be equipped with more pins to receive signals of the mechanically-driven switch 28. This reason also complicates the circuit design and increases cost.